1. Field of the Invention
The present invention relates to a method of connecting plates of an electrode to a terminal of a storage cell, in particular a rechargeable lithium storage cell with spiral-wound cylindrical electrodes. The invention also relates to a storage cell obtained by the method.
2. Description of the Prior Art
A storage cell with spiral-wound electrodes incorporates electrodes in the form of tapes wound around a central former or spool to form a cylinder. Each electrode includes a metal current collector, at least one face of which supports the active material of the electrode. Each electrode is electrically connected to a current output terminal which provides electrical continuity between the electrode and the load with which the cell is associated.
The terminal passes through the container of the cell: the part outside the container receives the external connections and the part inside the container is connected to the electrodes. The terminal can be fastened or attached to the container. There are various ways to make the electrical connection between an electrode and a current output terminal. One way uses one or more conductive thin metal strips also known as plates: one end of each plate is welded to the edge of the collector and the other end is welded to the internal part of the terminal inside the container.
FR-A-2752089 describes a method of connecting the plates of an electrode of a storage cell of the above kind to a terminal attached to its container. The portion of the terminal inside the container includes a cylindrical shoulder. The method consists of assembling the plates around the periphery of the shoulder by means of a cylindrical member that is moved concentrically toward the periphery of the shoulder. The plates are then fixed to the periphery of the shoulder, in particular using a ring or electrical or ultrasound welding.
The above method has the drawback of a long fabrication time. Also, electrical or ultrasound welding does not provide sufficient quality in the case of welding aluminum plates to aluminum terminals, for example. Electrical welding is difficult to carry out, especially when a plurality of plates overlap, because there is then a cumulative contact resistance between the various plates and the terminal such that electrical welding becomes impossible or at least the weld obtained is of mediocre quality and does not provide a reliable mechanical and electrical connection between the plates and the terminal. The drawback of ultrasound welding is that it cannot be used to weld the plates to the terminal in succession because the vibration generated when welding a given plate degrades or destroys the weld attaching the previous plate.
An object of the present invention is to eliminate the above drawbacks of the prior art.
To this end, the present invention proposes a method of connecting plates of an electrode to a terminal of a storage cell, the method including:
clamping the plates between a holding member and the terminal, and
transparent laser welding the plates to the terminal through the holding member.
The plates are preferably each from 50 xcexcm to 80 xcexcm thick. The holding member is preferably from 0.5 mm to 1 mm thick.
In one embodiment the terminal, the plates and the holding member are made of aluminum. Alternatively, the terminal and the plates are each made from a material chosen from copper, nickel-plated copper and nickel and the holding member is made from nickel or nickel-plated copper.
In another embodiment the terminal has a cylindrical part and the holding member is a cylindrical ring with the same section, and:
the plates are clamped between the ring and the cylindrical part of the terminal, and
the plates are welded to the cylindrical part of the terminal.
In a further embodiment the terminal has a plane part and the holding member is plane, and:
the plates are clamped between the holding member and the plane part of the terminal, and
the plates are welded to the plane part of the terminal.
In this case, the method includes the step of bending the plates over the plane part from a peripheral edge of the plane part prior to clamping and welding. It is then advantageous if the terminal has a cylindrical part with the plane part on one face thereof and the holding member is a washer.
In another aspect the invention proposes a storage cell in which plates of an electrode are disposed between a terminal and a holding member and including at least one weld passing through the holding member and the plates and penetrating the terminal. The plates are preferably each from 50 xcexcm to 80 xcexcm thick. The holding member is preferably from 0.5 mm to 1 mm thick.
In one embodiment the terminal, the plates and the holding member are made of aluminum. Alternatively, the terminal and the plates are each made from a material chosen from copper, nickel-plated copper and nickel and the holding member is made from nickel or nickel-plated copper.
In another embodiment the terminal has a cylindrical part and the holding member is a cylindrical ring with the same section, and:
the plates are clamped between the ring and the cylindrical part of the terminal, and
the plates are welded to the cylindrical part of the terminal.
In a further embodiment the terminal has a plane part and the holding member is plane, and:
the plates are clamped between the holding member and the plane part of the terminal, and
the plates are welded to the plane part of the terminal.
In this case the plates are preferably bent over the plane part from a peripheral edge of the plane part prior to clamping and welding. It is then advantageous if the terminal has a cylindrical part with the plane part on one face thereof and the holding member is a washer.
Other features and advantages of the invention will become apparent on reading the following description of a preferred embodiment of the invention, which description is given by way of example only and with reference to the accompanying drawings.